lol what you mean its 1Gb + Its Geforce 
So i must change it 
Memory doesn't mean anything, and Geforce is just a brand.

I played GTA IV with GeForce 8400 GS... so should that mean that my GTA IV should run? It did, but uber laggy even on the lowest setting. with updates, it became 30 FPS. (and I had a Pentium 4 processor LOL!)
Change your video card to a more powerfull one, I guess that solves the problem. Also check which processor you have, a Quad core will help a lot... a dual core is also ok.